The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Coatings composing the charge-transporting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) have been developed for biomedical electronic devices such as neural probes. See Cui et al., Sensors and Actuators (2003) 89:92-102 which is hereby incorporated in its entirety. Although the morphology and conductivity of PEDOT make it useful as a bioelectrode coating, a more bioactive film would be preferable.
When a neural probe is contacted with a conductive polymer for example polythiophene or PEDOT or PEDOT derivative, inherent problems are easily found during in vivo use. When a probe is inserted into living tissue, for example, the brain, there is a reactive inflammatory response, because the electrode surface lacks the proper functionality to interact with the cells at the site of implantation.
Therefore, in order to maintain the recording and stimulating capabilities of neural devices, it is necessary to develop materials that reduce the brain immune response, increase the likelihood of establishing biocompatible connections between the electrode and the brain cells and materials that favor the attraction of neurons to the electrode over less favorable cell types like glial cells.
At present, electrodes comprising of PEDOT coatings have been designed to increase the total surface area of the electrode and enable the electrode to interact with fine cellular processes in order to make them more biocompatible. However, the present PEDOT coated electrodes are not sufficiently biologically compatible with the cells and tissues into which they are implanted.
PCT Application WO 2006/018643 describes sensors that comprise a conjugate having a ligand attached to EDOT or derivative and polymer thereof by means of a spacing element. This application illustrates an example of nucleic acid coupling to EDOT via the synthesis of an acid functionalized EDOT. The synthesis process yields a 2,3-dihydro-thieno[3,4-b][1,4]dioxin-2-ylmethyl ester which can be coupled to a nucleic acid using (dimethylaminopropyl)-3-ethyl-carbodiimide hydrochloride as a coupling agent. However, several drawbacks of using the ester or ether forms of carboxylic acid functionalized EDOT appear when used in a biological system. These drawbacks include enzymatic cleavage of the conjugated polymer at the ester bond by esterases, for example acetylcholinesterase, thus limiting the sensor or film's ability to interface with biological tissue. Also, since the ester form of carboxylic acid functionalized EDOT has a longer alky chain, it is less water-soluble than the carboxylic acid described in this application.
Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.